Simulations of crustal anatexis: Implications for the growth and differentiation of continental crust

There is overwhelming and incontrovertible petrological and geophysical evidence for the significant role played by mantle-derived mafic magma in the generation and growth of continental crust. Likewise, intrusion of mafic magmas beneath or into continental crust is very likely the major source of enthalpy that drives intracrustal differentiation. A simple dynamical model has been constructed to examine the critical factors that govern the evolution and time-scale of crustal anatexic events when driven by basaltic magma underplating or injection into crust. Critical factors include the intensity of the enthalpy input (i.e., the power dissipated) and the rheological properties, bulk composition and compositional structure of the source rocks undergoing partial fusion. We have performed numerical simulations to evaluate these factors using phase equilibria and thermochemical and transport property data applicable to the binary eutectic system CaAl2Si2O8 −CaMgSi2O6 as a rough analog to study anatexis of mafic lower crust. The role of enthalpy power is tested by varying the enthalpy (or temperature) along the base of the crustal block while maintaining a fixed temperature at the top. As ratio Tbot/Ttop increases modestly from 1.05 to 1.15, the average fraction of melt at steady state in the anatexic region increases from 50% to 75%. Time to attain steady state scales inversely with Tbot/Ttop with an increase by a factor of 2 for a 10% decrease in Tbot/Ttop. Typical